Escapement mechanism for typewriting and like machines



Jan. 2, 1951 2,536,619

H. c. YAEGER ESCAPEMENT MECHANISM FOR TYPEWRITING AND LIKE MACHINES Filed March 26, 1948 2 Sheets-Sheet l IN V EN TOR.

BY WM: I ATTORNEY Jan. 2, 1951 H c YAEGER 2,536,619

ESCAPEMENT MECHANISM FOR TYPEWRITING AND LIKE MACHINES Filed March 26, 1948 2 Sheets-Sheet 2 JNVENTOR.

72km; C Qge aez By 2940 ATTORNEY Patented Jan. 2, 1951 ESCAPEMENT MECHANISM FOR TYPEWRIT- ING AND LIKE MACHINES Harry 0. Yaeger, West Hartford, Conn, assignor to Underwood Corporation, New York, N. Y., a

corporation of Delaware Application March 26, 1948, Serial No. 17,256

6 Claims.

This invention relates to letter-feed escapement mechanisms for typewriting and like machines, and has for one of its objects the provision of an improved mechanism of this kind in which the vibrations incident to impact of the carriage in concluding each letter-feed or word-space step are dampened or absorbed, and the carriage is brought to rest terminating the typing cycle in the shortest period.

Another object is to provide an improved escapement mechanism capable of stepping the paper carriage in rapidly suceeding letter-feed increments such as is required in relatively highspeed typing, each step of feed being nevertheless concluded substantially free of vibration despite the fast carriage motion through each letter-feed form of a double-acting, oil dash-pot operatively connected to the two pawls. The arrangement is such that as the one pawl operates to control a step of the carriage, and the damping device cushions the stopping of the carriage, the other pawl is advanced in readiness to control the next step of feed and the damping device is brought to position in readiness to cushion the feed action of the other pawl in controlling the next step of the carriage.

With the above and other objects in view, the invention will now be described with reference to the accompanying drawings wherein two embodiments which the invention ma assume in practice are shown for the purposes of illustration.

In the drawings,

Figure 1 is a transverse sectional view of the typewriter embodying the invention, the section being taken on a fore-and-aft plane just rightward of the escapement mechanism,

Figure 2 is a fragmentary rear elevational view 1 condition obtaining incident to a step of letterfeed succeeding, or preceding, that shown in Figure 2,

Figures 4, 5 and 6. are enlarged detail views of the condition of the escapement mechanism in various stages of operation, Figures 4 and 6 corresponding respectively with Figures 2 and 3, and Figure 5 showing a condition during one letterfeed step, s

Figure '7 is a view similar to Figure 3 but showing a modification of the damping or friction device, and

Figure 8 is a sectional view of Figure '7.

Referring particularly to Figure 1, the typewriter embodying the invention as illustrated comprises a paper carriage 1 arranged to travel on rails 8 and supporting a platen 9 which, in conjunction with other devices not shown, holds the paper for typing by typebars l0. Depressing a type keylever ll, operating through a link, a sublever l2 and a second link, swings the associated typebar 10 toward the platen. As the typebar approaches the platen, a shoulder I3 thereon engages and actuates a universal bar l4 rearwardly. Bar I4 is carried by a frame l5 slidably supported for fore-and-aft movement at its forward portion in a typebar segment, not shown, and guided at its rear portion by a rockable bail l6 pivoted at l! on the typebar segment, the bail having arms to which frame I5 is articulated at [8. One of said bail arms has a link flexibly connected to it, which connects bail I6 to an arm 2| of a rockable frame 22 pivoted at 23 on a subframe 24 mounted on the mainframe of the typewriter. Frame 22 has a depending arm 25 to which is secured a member 26 forming an extension of said arm and having at its upper end a crank pin 21. As shown best in Figure 2, a bracket 28 secured to subframe 24 extends rearwardly therefrom to provide a pivot or fulcrum 30 for a lever 3| having a slot in which the crank pin 21 operates. A spring 32 anchored on subframe 24 and acting on link 20, restores the universal bar l4 and associated mechanism to the normal, inactive position.

The mechanism associated with the universal bar 14, thus far described, including mainly link 20, rockable frame 22, crank pin 21 and lever 3|, constitutes means operable by the typebars III or the type actions thereof for actuating the escapement mechanism to cause the carriage to step a letter-space for each type-impressing stroke. Word-spacing is effected by the usual space-bar-operated mechanism arranged to actaken on line 88 tuate the letter-feed escapement through mechaanism including part of the above-described actuating means. For this purpose the member 2% of the rockabl frame 22 extends forwardly and is engaged by an arm 33 secured to a cross shaft or bail 3Q pivoted at each end 35 on the mainframe. Arms 33, of which one is shown, reach forwardly from bail 34 and have at their forward ends the usual space bar, not shown.

In the two embodiments of the invention illustrated, the escapement mechanism has the escapement dogs cooperating directly with a rack 37 mounted on and traveling with the carriage I. It will be apparent, however, that the dogs may coact with an escapement wheel which, b the well-known means of a pinion and carriage-carried gear rack, is geared to the carriage to control its letter-feed and word-space travel. Either the escapement rack 3? or the escapement wheel mentioned, may be considered broadly as a toothed member that is movabl with the carriage. The carriage is impelled in the line-typing direction by the usual spring drum 38 and draw band.

The rack has its teeth spaced preferably at double the lstter-space pitch. That is, for a letter spacing of say one tenth inch, the pitch or spacing of the rack teeth is two tenths of an inch. As shown best in Figures 4-43, the rack 31 has two pawls or dogs it and ii cooperating therewith arranged parallel thereto and mounted for pivotal and limited endwise sliding movement on a stud secured to the subframe 24, each pawl having a slot engaging the stud and limiting the endwise movement or" the pawl in cooperation with the stud. At its free end each pawl has a, tongue projecting into an opening in a guide piece [l3 on subframe 2d, the opening guiding the pawls in their pivotal and sliding movements and limiting the upward movement to an extent such as to enable the pawls to coact with the rack, as latter described. Two springs one for each pawl it), are anchored on sub-frame 2s and ae connected respectively to a depending arm of each pawl. The arrangement of the springs and pawl arms is such that the pawls are urged leitwardly to the limits defined by the slots engaging stud 2, and tend to pivot upwardly toward rack El to the extent determined by the engagement of t -e pawl tongues against the upper end of the opening in guide 63.

Each pawl id, 5, has a prong d5, 16 which projects rightwardly, as viewed in Figure 2, or in the direction of line-typing carriage movement. A pawl tripper l? is flexibly connected to the actuating lever iii in such manner as to enable the tripper to oscillate in planes parallel to and transversely of lever 35. At its upper end, tripper ll is bent transversely to provide a lug cooperative with the prongs 35, 56. A spring 5! anchored on subframe E i tends to pull tripper dl upwardly and leftwardly as viewed in Figure 2. An adjustable stop screw 52 on the subframe engages tripper cl to determine its leftward po sition. A slot in an angle piece 53, through J which the tripper ll projects, guides the upper end of the latter against fore-and-aft displacement so that the lug 5G is maintained in align ment with the pawl prongs it.

A bracket plate 5 3 is adjustably secured on the subframe 2% by screws 55 extending thru slots in the plate. Plate provides a pivotal mounting for two bell crank levers 56, 5? which constitute an operative connection between the pawls 49. ll and a, friction or clamping device.

In the modification shown in Figures 1 to 6, this dampin devices takes the form of a doubleacting oil dash-pot, indicated generally at 58. As hereinafter described in further detail, each pawl Qi is alternately effective to control successive letter-feed steps of the carriage, incident to which the then effective pawl is moved endwise rightwardly from an advanced position to a limited extent which determines the length or the letter-feed step. This rightward, letterfeed-limiting stroke of each pawl is snubbed or cushioned by the dash-pot device 58.

A pin 53 on pawl 40 is adapted to engage one arm of bell crank 56, the other arm of which engages a groove in a member Bl adjustably held on a piston rod 62 on which a piston 63 is secured. The piston 33 is slidably fitted in a closed cylinder'or dash-pot 54 having a cylinder head :35 through which the piston rod 52 passes. The cylinder 6% is filled, or partly filled, with suitable non-compressible liquid, preferably oil of a suitable viscosity.

Bell crank 5! has an upstanding arm offset to clear the near pawl 48, as viewed in Figure 2, with the end of the arm in the plane of the far pawl s! and engageable by the rightward end thereof. The two bell cranks 56, El are geared together by a toothed connection 6'! by which the rocking of one bell crank in one direction causes the other bell crank to rock in the opposite direction. The interconnection 67 between the bell cranks 56, 5i serves primarily to transmit the rightward, carriage-stepping stroke of pawl ti to the dash-pot device 53.

The several elevational views show the mechanism as viewed from the rear and therefore the stated directions of movement, leftward or rightward, of the escapement parts and the carriage are the reverse of those as they occur in the typewriter from the typists viewpoint.

The letter-feeding action of the rack 37 and the two pawls ts, 4i of the escapement mechanism will now be described, with reference particularly to Figures 4 to 6. Upon operating any of the type actions or upon operating the space bar for word spacing, the rockable frame 22 is caused to swing rightwardly as viewed in Figure 1, thus swinging crank pin 2'! downwardly and causing lever 3! to rotate counterclockwise about its pivot 3b and thereby pull tripper Al downward against the tension of its spring 5|. Before a letter-feed step occurs, the escapement mechanism may be considered as in the condition shown in Figure 4, although the condition of the mechanism as shown in Figure 6 may also be had at the start of the letter-feeding step. In Figure 4 it will be noted that pawl 49 is in control of the carriage, holding same against ri htward travel, and pawl 4| is in an advanced leftward position in read ness to control the next step of feed. As previously described, the teeth of rack 5:3! are at a pitch double that of theletterspace step or say two-tenths of an inch. Nevertheless each pawl, when effective, limits the step of the carriage to the actual letter spacing or one-tenth of an inch. In the embodiments shown, the actual endwise movement of each pawl is limited, by the length of its slot at stud G2, to about half a letter-feed step or onetwentieth or" an inch, the remaining portion of the letter-feed step being accommodated by the clearance between the advanced pawl and the next eifective tooth of rack 31. This will be evident in respect to the rearmost pawl 4|, in

' entry of the returning pawl ahead of the next rack tooth.

Referring again to Figure 4, it-will be seen that the'lug B of tripper 4'! overlies the prong 45 of pawl 40, and that pawl 4 I, being in its leftward or advanced position, has its prong 46 clear of the path of lug 5B. Thus, as tripper d! is pulled downwardly its lug 50 engages prong '45 and pulls pawl 40 clear of the rack tooth with which it was engaged, to the position shown in Figure 5. At this instant the carriage becomes free to travel in the letter-feed direction, impelled by the spring drum 38. As the carriage moves rightwardly, as viewed in Figure 5, the tooth of rack 37 just ahead of pawl 4| moves rightwardly until it becomes engaged with said pawl, after which pawl 4| moves endwise with the carriage until stopped by the bottoming of its slot on stud 42. As aforementioned, the aggregate of the initial motion of the rack tooth into engagement with the pawl, and the endwise movement of the pawl, determines the length of the letter-feed step. The carriage is thus stopped at the position where the next type may be impressed or where a word space occurs. During this action the tripper 41 may be in its lower position shown in Figure 5 so that as pawl 4| is moved rightwardly, its prong 46 engages the tripper lug 5|) and moves same off the prong 45 of the depressed pawl 40. If pawl spring 44 is amply strong to overcome the friction between prong 45 and lug 5D, pawl 40 may be shifted leftward by its spring as soon as its tooth is clear of the rack tooth with which it was engaged. Pawl 48 is thus moved upwardly and leftwardly and thereby assumes the position shown in Figure 6.

During the next step of letter-feed, the action of tripper 41 on the pawls 40, 4|, and the action of the pawls in controlling the letter-feed step, is substantially the same as that previously described except that now pawl 4| is released from the rack and pawl 41} assumes control of the ensuing letter-feed step.

It will now be seen that as the carriage takes a series ofletter-feed steps, the'pawls 40, 4| reciprocate back and forth alternately. As each carriage step occurs the piston 63 of the dash-pot device is moved in one direction, either up or down as the case may be, in response to the carriage-stepping control movement of the then ei fective pawl. With the escapement parts in the position shown in Figure 2, the rearward pawl dl is the one which next controls the carriage step. As a result of the preceding step of feed, in which pawl 45 controlled the step, the dash-pot piston was raised from the Figure 3 to the Figure 2 position by the action of bell crank 56 swinging clockwise as pawl 45 was rightwardly shifted. In the next step of feed, pawl 45 is released from the rack, the carriage thus starting the next letterfeed step, incident to which pawl 4| is moved limitedly rightward with the carriage, as afore described. During this movement of pawl 4!, bell crank 5'! is rotated clockwise and, thru the toothed connection 61, causes bell crank 55 to rotate counterclockwise and thereby force piston 63 downward. Pressure on the oil in the lower portion of cylinder 54, thus caused, tends to resist and thereby cushion the feed-controlling stroke of pawl 4|.

It may be here noted by reference to Figure 2 that a clearance may be provided between the rightward end of pawl 4| and bell crank 51. As shown in Figure 3, a similar clearance is provided for pawl 40 by locating pin 60 thereon so that it is clear of bell crank 56 when pawl it is in its leftward or advanced position. This clearance enables the pawls to move a limited degree before being subjected to thesnubbing effect of the damping device. A degree of free movement of each pawl may be desirable in order to have a greater portion of the feed step free of the snubbing action and thus attain the desired highspeed operation. The extent of free pawl movement may be varied to suit particular conditions and operating requirements, or may be eliminated entirely. Accordingly, the plate 54 is mounted so that by the adjustment provided at screws 55, which enables changing the location of plate 54 horizontally with reference to the pawls 40, 4|,

the clearance between each pawl and the corresponding bell crank 55, 51 may be adjusted.

The amount of resistance and the degree of cushioning or snubbing effect afforded by the dash-pot, where oil or other non-compressible liquid is used as the cushioning medium, depends largely on the rate at which the oil may bypass the piston from thepressure side to the opposite side thereof. A small aperture 88 may be provided thru the piston itself to afford a suitable bypass, if the piston has a very close fit in the cylinder; or the piston may be imperforate and a sufficient bypass may be afforded at the periphery of the piston by an adequately loose fit of the piston in the cylinder. The rate of oil fiow thru the bypass should be such that a pressure is built up that is adequate to retard the concluding part of the feed stroke of the pawl, and yet allows the differential pressure on the opposite sides of the piston to become substantially equalized as the letter-feed step is concluded.

The action of the dash-pot device 58 in a step of feed succeeding that just described, during which the near pawl Ail controls the step of feed, is substantially thesame as that of the preceding step. In this instance, however, the control stroke of pawl 40, acting on the dash-pot piston 63 directly thru the medium of bell crank 55, causes the piston to be raised from the Figure 3 to the Figure 2 position, the cushioning pressure at this time being generated at the upper portion of dash-pot cylinder 64. As pawl 48 approaches the completion of its stroke, its rate of movement is substantially decelerated by the built-up differential pressure, which pressure is gradually dissipated by the oil bypassing the piston.

The second embodiment or modified form of the invention shown in Figures 7 and 8 will now be described. Instead of the dash-pot device of the first form, a friction device it! of the mechanical braking type is provided. The bell crank 55 has a fiat plate-like arm H in which a slot '52 is provided. The bracket plate Ed on which the bell cranks 55, 55 are pivoted, extends left ward and has a screw 13 threaded therein and projecting thru slot '52. Between arm H and bracket plate 55 a washer M is installed and a spring disc 15 backed by the head of screw 13 exerts a pressure against arm H. The pressure of disk 75 imparts a frictional resistance to the rocking of bell crank 55, which is also eifective on bellcrank 5'! thru the toothed connection 61. It will be apparent that the friction device 10 acts in substantially the same manner as does the dash-pot device 58, to impart a snubbing or damping effect to each escapement pawl 40, 4| during the letter-feeding action of that pawl. As the two pawls are alternately shifted rightward incident to their step-controlling action, arm H is oscillated, first one way and then the other, each oscillation being retarded or braked by the friction of disk 15 and washer 14 on the arm. The feed stroke of the then-effective pawl is thus snubbed or brought to a more gradual stop, with the result that the usual impact and attendant vibrations are dampened and the resultant noise of escapement operation is materially reduced.

A backspacing mechanism is provided whereby upon depressing the usual backspace key the carriage is caused to step back one letter space for each key depression. The mechanism disclosed herein is similar to that described and claimed in the I-Ielmond Patent No. 1,630,384 to which reference may be had for a more detailed description.

Referring to Figure 1, a backspace keylever 16 is secured to a rockable shaft 1'! from which projects an arm '18, a spring 19 urging the keylever 76 and arm 18 clockwise. A link 8|] articulated to arm 18, is flexibly connected to a backspace dog 8|, Figure 2, pivoted at 82 on a dog carrier 83. Dog carrier 83 is pivoted at 84 on the subframe 24 and carries a leaf spring 85 pressing on a fixed stop 86 to urge the dog carrier leftward, as viewed in Figure 1. Stop 86 also limits the leftward swing of carrier 83. Spring 85 tends to react against the force of spring 19 but, being substantially weaker than spring '19, allows the latter to urge the dog carrier 83 to its normal rightward limit, spring 85 serving mainly to eliminate any back lash in the linkage connection between the dog carrier 83 and arm 18. Before operating the backspace keylever, the dog 3| is rearward of, and out of the path of, rack 31. Upon depressing the backspace keylever i5, link 80 is drawn downwardly against the force of spring 19 and first causes the dog carrier 83 to swing leftwardly to its limit, assisted by spring 85. As shown in Figure 2, the backspace dog 8| has two letter-spaced teeth, instead of the conventional single tooth, to compensate for the double spacing of the teeth of rack 31. The leftward swing of dog carrier 83 moves dog 8| into the path of rack 3'! and engages one or the other of the teeth of the dog with the adjacent tooth of rack 31. After the dog carrier 83 reaches its leftward limit, link 8!], continuing downwardly, now reacts on the dog 8| causing same to swing about its pivot 82, leftward as viewed in Figure 2, a limited degree sufiicient to space the carriage backward one letter-feed step.

The extent of backspace movement imparted to the carriage by the dog 8| should, of course, be such that when escapement pawls 46, 4! resume control, the carriage is one letter space back of its prior position. Because of the use of a double pitch rack and alternately effective pawls, each reciprocating about half a letter space, this backspace movement should be slightly more than one and a half letter spaces. This is necessary in order to allow the then idle escapement pawl 48 or 4| to take control of the carriage upon releasing the backspace keylever. To demonstrate this it may be assumed that before the backspace operation begins, the escapement mechanism is in the position shown in Figure l, in which pawl 40 is in control of the carriage. As the carriage begins its backspace movement leftward, pawl 40 will move leftward with the carriage to its limited extent of about half a letter space, As the carriage continues to move back, the rack tooth that had been engaged with pawl 40 now ratchets past pawl 4| and snaps up in back of that rack tooth. When this occurs the carriage has moved the necessary extent for backspacing and, upon release of the backspace keylever, will settle forward into its actual letter-feed position under the tension of spring drum 38. During this settling, the rack tooth behind which pawl 4| has ratcheted moves forward or rightward to the extent determined by the limited permissible movement of pawl 4|, at which time the carriage is at rest, the mechanism assuming the condition shown in Figure 6.

I claim:

1. In a typewriting machine having a paper carriage urged to travel in letter-feed direction, a letter-feed escapement mechanism comprising, a toothed member movable with the carriage, two feed pawls coacting with said toothed member to control the carriage travel in letter-feed steps, means acting on said feed pawls to cause an escapement operation defining each letter-feed step, said pawls being alternately bodily movable by the toothed member incident to successive steps of feed, and friction means for snubbing at least a part of the feed movement of each of said pawls.

2. In a typewriting machine having a paper carriage urged to travel in letter-feed direction, a letter-feed escapement mechanism comprising, a toothed member movable with the carriage, two feed pawls coacting with said toothed member to control the carriage travel in letter-feed steps, means acting on said feed pawls to cause an escapement operation defining each letter-feed step, said pawls being alternately bodily movable by the toothed member incident to successive steps of feed, and means including a single friction device common to both said pawls to dampen at least a part of the feed movement of each of said pawls.

3. In a typewriting machine having a paper carriage urged to travel in letter-feed direction, a letter-feed escapement mechanism comprising, a toothed member movable with the carriage, a pair of feed pawls coacting with said toothed member to control the carriage travel in steps of letter feed, said pawls being arranged for pivotal movement and for alternate limited movement bodily with the toothed member incident to controlling successive letter-feed steps, means acting on said pawls to cause each pawl to alternately escape the toothed member, and means including a non-compressible liquid medium for cushioning at least a part of the feed movement bodily of each of said pawls.

l. In a typewriting machine having a paper carriage urged to travel in letter-feed direction, a letter-feed escapement mechanism comprising a toothed rack movable with the carriage, a pair of feed pawls arranged parallel with said rack and coacting therewith to control the steps of letter feed, said pawls being mounted for pivotal movement to and from engagement with said rack and for limited endwise movement bodily with said rack, spring means urging said pawls in a counter letter-feed direction and toward said rack, means to cause said dogs to alternately escape the teeth of said rack, a dash-pot device operable in alternate directions, and means operatively connecting each of said pawls to said dash-pot device, to efiect a cushioning of the to eachstep of feed.

having a paper r-feed direction,

ith the carriage, arallel with said control the steps ng mounted for engagement with ment bodily with said pawls in a and toward said sj to alternately esingle friction device two levers operaposite directions being connected A nd the respective lever being engageable in'on direction by the feed pawls, said levers and friction device operating to efiect a sh lgbing action of the respective pawls incident ach step of feed.

6. ma typewriting ma having a paper if; L urged to travel intter-feed direction, a lette eed escapement Iii hanism comprising a toothed rack movable with the carriage, a pair ing a toothed rack movabl a pair offi'eed pawls arrang rack and cjoacting therewith" of letter feed, said pawls pivotal movement to and fr and for limited m counte' ';letter-feed directio rack, eans to cause said pa of feed pawls arranged parallel with said rack and coacting therewith to control the steps of letter feed, said pawls being mounted for pivotal movement to and from engagement with said rack and for limited movement bodily with said rack, spring means urging said pawls in a counter letter-feed direction and toward said rack, means to cause said pawls to alternately escape the teeth of said rack, a single dash-pot device operable in alternate directions, two bell cranks geared together to rotate in opposite directions respectively, one of said bell cranks being connected directly to said dash-pot device, and the respective bell cranks being engageable in one direction by the respective feed pawls, said bell cranks and dash-pot device operating to effect a snubbing action of the respective pawls incident to each step of feed.

HARRY C. YAEGER.

REFERENCES CITED Name Date Thompson et al. M Mar. 19, 1935 Number 

